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Monday, June 22, 2015

Can we harvest icebergs for fresh water yet?

June 19, 2015

Dear Cecil:

My lawn slowly dies as we here in southern California suffer another drought and our water agencies reduce deliveries to a slow dribble. Is it technically and economically feasible to harvest icebergs as a fresh-water source? Answer soon, as we're tired of Navy showers and unflushed toilets!

— Marvin Gardens

Cecil replies:

If shower duration is your primary concern right now, the drought may be making your whiskey-and-waters a little too strong. California accounts for about 11 percent of U.S. agriculture by revenue and 12 percent of the nation’s GDP overall. When you guys run out of water, we’re all screwed. We may never see an almond again.

Which makes the iceberg idea pretty appealing. With global warming well under way, icebergs should be breaking free and floating past our coasts any day now — and corralling one or two giant frozen chunks of fresh water certainly sounds easier than reducing the excess consumption of several metropolitan areas, or addressing the obvious problems with growing massive amounts of high-water-demand food under semi-arid conditions.

And the idea’s not new: proposals along these lines had already been kicking around for a few decades when the Saudi prince Mohammed al Faisal got into the act in the mid-70s. Seeking water for his country that didn’t have to be desalinated, he formed a company to harvest Antarctic icebergs and tow them up to the Red Sea. Unfortunately the plan stalled, in part because of difficulty balancing fuel economy with enough towing speed to keep the berg from melting en route. Icebergs haven’t changed much since then — they’re still unwieldy, slippery, dirty, and melty. But the tech’s gotten better, and we’re desperate, so let’s look at the process.

Step one: Get a lawyer. Most legal opinion appears to agree that bergs are generally available on a first come, first served basis, but it’s possible that either the United Nations (under the Convention of the Law of the Sea) or the Coast Guard might intervene in an ice-towing scheme — the latter is in charge of enforcing not only marine commerce safety regulations but also the U.S. Antarctica Conservation Act. Greenpeace could conceivably have some beef with iceberg towing, as might various other environmentalist groups.

Step two: Scout a suitable iceberg. What you want is a tabular iceberg — flat top, longer than it is tall — weighing maybe a million to 10 million tons. There are more of these in Antarctic waters than in the north Atlantic, plus there aren't any polar bears on them; on the other hand, using an Arctic iceberg may save money by minimizing towing distance. If the right berg doesn’t already exist, explosives may be needed to break a usable hunk off an ice shelf or glacier.

Step three: Move it. While we currently use tugboats to nudge icebergs away from oil tankers, imparting more long-term direction is trickier. A few years ago, a group of researchers led by Georges Mougin, Prince Faisal’s engineering guru from the 70s, used 3D-modeling software to simulate towing a 7.7 million-ton tabular iceberg from Newfoundland to the Canary Islands. The team calculated that a single tugboat attached to a giant kite, if aided by winds, currents, and Mary Poppins, could do the job in 141 days.

What about the melting issue? Ice (bergs included) readily melts in water, even more so when it’s being dragged around. Several solutions have been proposed to deal with this. Team Mougin favors wrapping a “skirt” of geotextile — synthetic fabric typically used to prevent soil erosion or improve drainage — around the entire submerged portion of the iceberg to insulate it from the warmer water. (Remembering that nine-tenths of an iceberg famously lurks below the surface, that’s a lot of geotextile.) Even so clad, the simulated iceberg loses 38 percent of its original mass in transit.

Step four: Start making sacrificial offerings to Poseidon, because that’s really all we can do at this point to prevent catastrophe. Icebergs aren’t structurally homogenous and can easily shatter under stress. Keeping tow cables secured to an object whose shape is constantly shifting will also be difficult, and an unexpected storm could set the berg drifting toward cruise ships, commercial vessels, wildlife refuges, or seaports. Cue The Perfect Storm, but with an iceberg crashing into Newport Beach.

Step five: Attempt, probably in vain, to limit the energy required to transform the iceberg into usable water. Since we can’t haul the entire berg up on land, the ice will have to be cut up (using heated wires or tubes) and melted offshore and the water transported as needed, which turns out to be labor-intensive and costly. It’s just not particularly easy to cut up a lot of ice, as anyone who’s tried to chisel a frozen hulk in the freezer into individual cubes knows well. Finally, any water slated for human consumption would require treatment to remove pollution, penguin poop, etc., but even water for agricultural use will likely need some desalinization.

Needless to say, none of this has reached a level of obvious practicality. I think it’s safe to say that if it’s yellow, you’re going to have to let it mellow for a while yet.